Western Digital has extended its My Book line of hardback-like external hard drive units with model incorporating an eSATA port alongside the customary USB 2.0 connector.

It's all in the name of speed, of course. SATA is the new standard for connecting hard drives internally within a computer, but a fair few motherboards - not to mention add-in cards - are appearing with a version of the interconnect technology for external drives.

The My Book Premium ES' eSATA has a maximum throughput of 3Gbps, but WD said data with move back and forth between drive and computer at 2.4Gbps, still rather more than the 480Mbps maximum USB 2.0 offers.

The drive ships with EMC Retrospect Express HD 2.0 back-up software, and automatically shuts down and powers up when you disconnect and reconnect your computer. Initially available in the US, the My Book Premium ES is available in 320GB and 500GB versions for $179 and $229, respectively.